1. Field of the Invention
The present invention relates to an electrically operated pump assembly comprising a pump, an electric motor for driving the pump and a control circuit for controlling the rotating speed or the like of the electric motor, and more particularly, relates to such an electrically operated pump assembly disposed in a vehicular fuel tank and adapted to feed fuel in the tank to an engine.
2. Description of the Prior Art
It has been often desired to increase or decrease the discharge quantity from an electrically operated pump. For example, when such a pump is used to feed fuel to a vehicular engine, it is desired to provide a larger discharge quantity when the engine requires more fuel, while it is desired to provide a smaller discharge quantity when the engine requires less fuel. In order to meet such a requirement, the prior art has proposed a technique of using a control circuit for increasing or decreasing the rotating speed of an electric motor. It is also known in the prior art to use a brushless motor for driving the pump, and in this case, a control circuit for switching the exciting phase of the brushless motor is required.
The prior art has also proposed a technique of enclosing the control circuit in a housing in which a pump section and an electric motor section are integrally disposed, and such a technique is disclosed in Japanese Utility Model Publication No. 4-48143 (Japanese Laid-Open Utility Model Publication No. 62-172272), Japanese Laid-Open Utility Model Publication No. 2-99288 and Japanese Laid-Open Patent Publication No. 56-88982. According to the technique disclosed in the above-mentioned Japanese Utility Model Publication No. 4-48143 and Japanese Laid-Open Utility Model Publication No. 2-99288, the control circuit is enclosed in an air-tight container which is installed in the housing, so that fuel pressurized by the pump section flows around the air-tight container. The control circuit includes a power transistor or the like which produces heat during operation thereof. Flow of fuel around the air-tight container can effectively cool the control circuit. Japanese Laid-Open Patent Publication No. 56-88982 discloses a technique of completely separating the control circuit from fuel by means of an insulating material, having no means provided for cooling the control circuit.
Such an arrangement as to enclose the control circuit in the air-tight container around which fuel flows is effective to cool the control circuit. As the liquid in the housing is, however, highly pressurized by the pump section, the air-tight container must be constructed strong enough to stably protect the control circuit from the high pressure liquid for a long period of time. In practice, however, sealed portions of the air-tight container are apt to be broken by the high pressure liquid, which will cause intrusion of the liquid into the air-tight container, resulting in possible damage to the control circuit or inoperativity thereof.
In case the control circuit is completely separated from the high pressure liquid by means of the insulating material, heat transfer from the control circuit to the liquid is prevented, disadvantageously causing possible accumulation of heat in the control circuit.